1. Field of the Invention
The present invention relates to a viscous heater for generating heat by a shearing a viscous fluid which is subjected to a heat exchange with a heating fluid as a heat source of a heating apparatus.
2. Background of the Invention
Japanese Unexamined Utility Model Publication No. 3-98107 discloses a viscous heater of a variable capacity, provided with front and rear housings facing and connected with each other so as to form a heat generating chamber, and a water jacket located around the heat generating chamber. The housing is formed with an inlet port for introducing the heating water (fluid) into the water jacket and an outlet port for taking out the heated water from the water jacket to an outside heating circuit. A driving shaft is rotatably supported by the front and rear housings via respective bearing units, while a rotor is connected to the shaft in such a manner that the rotor rotates in a heat emission chamber. The heat emission chamber and the rotor have faced inner and outer surfaces, on which surfaces labyrinth grooves, which are located adjacent with-each other, are formed, while a gap is formed between the confronting surfaces, so that a viscous fluid, such as a silicone oil, is filled in the gap.
The viscous heater is further provided with a diaphragm unit arranged at a location below the front and rear housings and has upper and lower covers and a diaphragm arranged between the upper and the lower covers, so that a control chamber is formed on one side of the diaphragm. The front and rear housings are, at their top parts, formed with vent holes which are in communication with an atmosphere, while the upper and lower covers are formed with communication pipes, which are in communication with the control chamber. An arrangement of the diaphragm is such that the inner volume of the control chamber is controlled in accordance with various factors, such as an intake vacuum and a spring force of a coil spring.
The viscous heater is incorporated into a heating device for a vehicle such that a rotating movement of a crankshaft of an internal combustion engine of the vehicle is transmitted to the driving shaft, which causes the rotor to be rotated in the heat emission chamber. As a result, shearing of the viscous fluid occurs in the gap between the confronting surfaces, resulting in the generation of heat, which is subjected to a heat exchange with the water recirculated to the water jacket, so that the recirculated water is heated and is used at the heating circuit for executing a heating operation.
In Japanese Unexamined Utility Model Publication No. 3-98107, in order to vary the capacity of the viscous heater, when the degree of the heating is too strong, the diaphragm is moved downwardly by the action of the manifold vacuum, which causes the volume of the control chamber to be increased. As a result, the viscous fluid in the heat generating chamber is recovered to the control chamber, so that the heat generating amount at the gap between the confronting surfaces of the heat generating chamber and the rotor is reduced, thereby weakening the heating. Contrary to this, when the degree of the heating is too weak, the diaphragm is moved upwardly by the action of the manifold vacuum and the force of the spring, which causes the volume of the control chamber to be decreased. As a result, the viscous fluid in the heat generating chamber is issued to the heat generating chamber, so that the heat generating amount at the gap between the confronting surfaces of the heat generating chamber and the rotor is increased, thereby strengthening the heating.
In the prior art structure of the viscous heater, recovery of the viscous fluid from the heat generating chamber to the control chamber causes air to be introduced into the heat generating chamber via the vent hole, thereby canceling an occurrence of a vacuum in the heat generating chamber. In other words, contact of the viscous fluid with the newly introduced air is occurs every time when a reduction of the heating capacity is occurs, thereby speeding-up degradation of the viscous fluid.
Furthermore, in the prior art structure, the volume of the control chamber, which is under an expanded condition, is equalized to the volume of the heat generating gap between the inner surface of the heat generating chamber and the outer surface of the rotor. Thus, a limited amount of the viscous fluid is merely moved between the control chamber and the heat generating chamber in accordance with the expansion or contraction of the control chamber. Thus, it is likely that a particular part of the viscous fluid is subjected to shearing at the heat generating gap. Thus, a quick degradation of the viscous fluid is likely to occur.